1. Field of the Invention
The object of the invention is to optimize the thermal insulation of equipment, in particular cryogenic equipment, by the use of several insulation technologies on one and the same item(s) of equipment or on one and the same set of equipment.
2. Related Art
For cryogenic applications, the insulation technology offering at the present time the best compromise is often the cold box, as described in “Tieftemperaturtechnik [Cryogenics]”, 1985, pages 490-495.
A cold box is a structure (which is generally parallelepipedal) containing the equipment to be insulated and filled with an insulation, generally in powder form (one of the insulations most frequently used in cryogenics is perlite). This insulation generally fills the entire space between the items of equipment and the entire space between the equipment and the structure.
The main functions of the structure are:                to support the insulation; and        to partly support the equipment.        
The main functions of the insulation are:                to limit the heat losses between the items of equipment and the outside; and        to limit heat exchange between the items of equipment.        
When designing a cold box, the insulation technology chosen is a compromise between several constraints:                safety (compatibility of the insulation with the products to be insulated, etc.) and the environment (toxicity of the insulation, end-of-life recycling, etc.);        the absence or slight presence of frosting, which may accelerate wear of the equipment and pose safety problems;        accessibility to the equipment;        investment cost; and        loss of energy, divided into:                    specified heat loss to the outside            specified heat exchange between the various items of equipment in the box.                        
One of the advantages of a cold box is that it insulates a set of equipment overall (within the context of this patent, the term “equipment” includes all items to be insulated, including any pipework) instead of having to insulate the items of equipment one by one, hence making a substantial saving in time and labour as regards investment cost.
Among the drawbacks, the following may be noted:                the need to construct an external structure for supporting and containing the insulation. This structure is particularly bulky and expensive. Its cost is, to a certain extent, proportional to its volume, the latter depending in particular on:                    the size of the equipment,            the space required to fit the equipment and            the necessary thickness of insulation;                        the accessibility of the equipment, which is restricted in operation (in particular when an insulation in powder form is used). This is because, to gain access to an individual item of equipment, it is often necessary to drain off a large amount of insulation.        